It has previously been suggested to use certain phenylphosphine palladium halide catalysts in reactions where water, primary alcohols or secondary alcohols together with carbon monoxide are added across ethylenic or acetylenic bonds of a wide variety of organic compounds to form corresponding acids or esters. In U.S. Pat. No. 4,257,973, for example, a method for making carboxylic compounds from aliphatically unsaturated organic compounds is disclosed. This method comprises the catalytic carboxylation or alkoxy carbonylation of the unsaturated compound through the addition of carbon monoxide and a hydroxy compound (preferably having one to four primary or secondary hydroxy groups) or water. According to U.S. Pat. No. 4,257,973, the reaction should be conducted at a temperature 35.degree. C. and 200.degree. C. at pressures of one to one thousand atmospheres in the presence of a catalyst composed of an organophosphorus palladium halide compound and 0.5 to 5 moles per mole of palladium compound of a metallic halide promoter. According to the disclosure U.S. Pat. No. 4,257,973, the preferred organophosphorus palladium halide compound is represented by the formula (PR.sub.3).sub.2 PdXY wherein:
X is chlorine or bromine; PA1 Y is hydrogen, chlorine, bromine, alkyl of 1 to 5 carbon atoms, aralkyl, acyl of 2 to 4 carbon atoms, or aryl of up to 12 carbon atoms; PA1 Each R is selected from lower alkyl, cycloalkyl of 3 to 8 carbon atoms, lower alkoxy, aryl of up to 12 carbon atoms, substituted with up to 3 halogen atoms or lower alkoxy groups, aryloxy groups of up to 12 carbon atoms, arylthio of up to 12 carbon atoms, aralkyl of up to 12 carbon atoms, lower alkylthio, di(lower alkyl) amino pyrrolidino, piperidino and vinyl groups; and PA1 with the proviso that not more than one aryl group attached to phosphorus contains a substituent in a sterically hindered position. PA1 where each R' is selected from lower alkyl of 1-5 carbon atoms; lower alkoxy of 1-5 carbon atoms; fluorine; chlorine; phenyl or napthyl, including, substituted derivatives thereof; cyano; nitro; fluoro alkyl of 1-5 carbon atoms, chloro-alkyl of 1-5 carbon atoms; dialkyl amino of 1-5 carbon atoms and thioalkyl groups, and hydrogen; PA1 where X is chlorine, iodine or bromine; PA1 where Y is hydrogen, chlorine, iodine, bromine, lower alkyl aralkyl, or acyl of 2 to 4 carbon atoms or aryl of up to 12 carbon atoms; PA1 where Z is selected from lower alkyl; cycloalkyl of 3 to 8 carbon atoms; lower alkoxy or aryl of up to 12 carbon atoms substituted with up to 3 halogen atoms or lower alkoxy groups; aralkyl groups of up to 12 carbon atoms; arylthio groups or aryloxy groups, each of up to 12 carbon atoms; lower alkylthio; di(lower alkyl)amino; pyrrolidino; piperidino groups and vinyl groups, PA1 with the proviso that the phosphine ligand cone angle of said palladium compound is between 170.degree. and 180.degree..
In accordance with U.S. Pat. No. 4,257,973, the promoter should be a chloride of Ti, Tl, Ni, Fe, Cr, Mn, Cu, Pd, Zn or Co or halide compound of Sn.
U.S. Pat. No. 4,257,973 (assigned to Dupont) states that not more than one of the aryl groups should have a "substituent" in a "sterically hindered" position "i.e., in an adjacent [ortho] position on the ring system or in the peri position in the naphthalene series". While U.S. Pat. No. 4,257,973 does not specifically define the type of "substituent" referred to, the only ortho substituted phenyl phosphine palladium catalysts disclosed in this patent have methyl substituents. Both Examples 14 and 16 disclose ortho-methylphenyldiphenylphosphine(o-tolyldiphenylphosphine) catalysts, with and without additions of tin chloride (see Table 1 of U.S. Pat. No. 4,257,973). Uses of these catalysts are reported as resulting in 1 hexene conversions of only 5% and 2% respectively. One of ordinary skill in the art thus recognizes that U.S. Pat. No. 4,257,973 leads away from the use of phenyl phosphine catalysts which exhibit greater steric hinderences than those of these mono o-methyl substituted phenyl phosphines.
It is known that various properties effect the catalytic nature of phosphorus ligands. In "Steric Effects of Phosphorus Ligands In Organometalic Chemistry and Homogenous Catalysis", by Chadwick A. Tolman, Chemical Reviews 77:3, 313-348, the electronic and steric effects of changing substituents on phosphorus ligands are discussed in detail. In this article Tolman teaches that catalytic effects caused by changing part of a molecule are electronic, as a result of transmission along chemical bonds, and/or steric, as a result of forces (usually non binding) between parts of a molecule. Tolman discloses that an electronic parameter v may be conveniently used to rank various phosphorus ligands in an electronic series based on CO stretching frequencies, and that v is indeed a measure of such electronic effects. Tolman also discloses that phosphorus ligands can be characterized according to their ligand cone angles (theta) and that the steric parameter is important, at least in those instances where the behavior of a given phosphorus ligand cannot be adequately explained in terms of electronic parameters. Accordingly, Tolman discloses various procedures for calculating the ligand cone angle (theta) of given phosphorus ligands. For example, the phosphine ligand cone angle of o-methylphenyldiphenylphosphine(o-tolyldiphenylphosphine), as calculated using Tolman's method, is 161.degree.. By way of comparison, triphenyl phosphine is calculated to have a phosphine ligand cone angle of only 145.degree., and tri-o-methylphenylphosphine(tri-o-tolylphosphine) to have a cone angle of 194.degree..
Heretofore, considerable attention has been directed to the preparation of unbranched carboxylation products. For example, U.S. Pat. No. 3,904,672 discloses the preparation of linear alpha-unsaturated fatty acid derivatives from the reaction of 1-alkynes and carbon monoxide in the presence of a hydroxylated coreactant and a homogenous ligand-stabilized noble metal-group IVb metal halide catalysts complex. Such reactions are described as producing the desired linear, alpha-unsaturated fatty acids or esters in "good yield free from substantial quantities of branched chain and other undesirable by-products".
In U.S. Pat. No. 3,455,989 (1981) entitled "Carbonylation of Olefinically or Acetylenically Unsaturated Compounds", other methods for the production of carboxylic acids or carboxylic esters are disclosed which comprise the use of olefinically unsaturated compounds which are reacted with carbon monoxide and water or alcohols or phenols at elevated temperatures. In this patent, the best results were obtained using phosphines containing at least one aromatic radical, particularly triarylphosphines such as triphenylphosphine, tri-o-cresylphosphine, tri-p-methoxyphenylphosphine, tributylphosphine, diphenylmethylphosphine and phenyldibutyl carboxylic esters.
Isobutyric acid and its esters are valuable intermediates in the synthesis of methyl methacrylate from propylene. The reaction of CO with olefins catalyzed by palladium salts ordinarily gives more straight-chain carboxylic acid products than branched-chain products. The commercial value of reactions producing isobutyric acid depend, however, on the ability of such reactions to achieve high ratios of branched (isobutyric acid) to normal (n-butyric acid) products. Using the phenyl phosphine metal halide catalytic methods many prior art methods have failed to achieve branched to normal ratios of greater than about 2.0-2.6. For example, in German Offenlegunschrift 2,739,096, 90% isobutyric acid ester selectivities were obtained when AlCl.sub.3 and HCl were added to a number of arsine-stabilized palladium catalysts, however the highest branched to normal ratio achieved using phosphine ligands was only 2.5. In "Carbonylation of Olefins Under Mild Temperature Conditions in Presence of Palladium Complexes", by Bittler et al, Angew. Chem., Int. Ed. 7:329 (1968), catalytic activities of different palladium salts in olefin carbonylations were reported using bis(triphenylphosphine)palladium dichloride to achieve 60% branched-chain ester and 30% straight-chain ester. Similarly, in U.S. Pat. No. 3,437,676 (1969) both bis(phosphine)palladium dichloride and tetrakis(phosphine)palladium(o) with HCl were reported to be catalysts capable of producing branched-to-normal isomer ratios of approximately 2:1. Lower proportions of branched-to-normal isomers are reported in U.S. Pat. No. 3,723,486 (1:1 mixture of methyl i-butyrate and methyl n-butyrate) and U.S. Pat. No. 3,793,369 (also a 1:1 mixtures of these butyrates). See also G. Cavinato and L. Toniolo, J. Mol. Catal. 111 (1979) and J. Mol. Catal., 161 (1981). Other patents disclose techniques which are described or relate to the optimization of straight-chain carboxylic acid products. See U.S. Pat. Nos. 3,530,155; 3,622,607; 3,641,071; 3,641,074; 3,652,655; 3,654,322, 3,661,949; 3,668,249; 3,700,706; 3,906,015; 3,501,518 and 3,968,133. Similarly, in "Noble Metal Catalysis II. Hydrocarbonylation Reaction of Olefins with Carbon Monoxide to Give Saturated Acids", by D. M. Fenton, J. Org. Chem., 38:3192 (1973) the effect of process conditions, solvents, and phosphine ligands on selectivity for normal carbonylation products is described, and a mechanism involving ortho-metallation of the phenyl phosphine ligand is proposed. See also J. F. Knifton, J. Org. Chem. 41, 2885 (1976).
Certain methods have been disclosed which lead to high branched-chain carbonylation products. In German Offenlegunschrift 2,701,354 a method is disclosed wherein isopropyl acetate is carbonylated with palladium chloride and a co-catalyst halide to isobutyric acid. Although the selectivity to the branched-chain product is high, the actual isobutyric acid yield is very low, probably due to the instability of the palladium catalyst in the absence of a Group Vb ligand. U.S. Pat. No. 4,245,115 (1981) discloses the conversion of olefins to esters or acids with a high ratio of iso to normal ester or acid by reaction of carbon monoxide with hydroxylic compound in the presence of a palladium salt complex with an arsine or stibine ligand as catalyst.
For descriptions of other carbonylation methods, please refer to G. Cavinato et al, Chimia, 33 286 (1979) (phenylphosphine palladium chloride catalyst system used with molecular hydrogen and solvent in propylene carbonylations to improve total ester yield), and to the following papers generally reporting asymmetric hydrocarboxylation of olefins by chiral palladium complexes: Botteghi, et al. Chimia 27:477 (1973); Consiglio et al, Gazz. Chim. Ital., 105:1133 (1975); Consiglio, Helv. Chim Acta., 59:124 (1976); Consiglio et al, Chimia 30:26 (1976); Consiglio et al, Chimia 30:193 (1976); Consiglio, J. Organomet. Chem. 132:C26 (1977); and T. Hayashi et al, Tetr. Lett. 3925 (1978).
Quite recently, some success has been reported in obtaining high branched product yields using phenyl phosphine catalysts. See U.S. Pat. No. 4,292,437. This patent, which is assigned to Dupont, discloses a process for the preparation of lower alkyl butyrate esters which is described as resulting in a higher percentage of isobutyrate products than has heretore been realized from phosphine liganded palladium catalysts. For example, U.S. Pat. No. 4,292,437 discloses the carbonylation of propylene by contacting the propylene and carbon monoxide with water or a lower alkanol of 1 to 4 carbon atoms in the presence of solvent and a palladium catalyst in complex with a ligand, "which improvement comprises an ortho-substituted ligand of the formula PAr.sub.3 wherein . . . the Ar moieties bear a total of one or two substituents in positions ortho to one or two carbon phosphorous bonds". (U.S. Pat. No. 4,292,437, Col. 1, lines 30-37, Col. 2, lines 1-3). These substituents are to be selected from lower alkyl of 1-4 carbon atoms, lower alkoxy and phenyl. The ligands are to be provided in a molar ratio to palladium of 4:1 to 122:1 and the process is to be conducted in the presence of a halide acid, such as HCl, HF, HBr or HI.
In U.S. Pat. No. 4,292,437, iso distributions of 81 and 92.5% for o-tolyldiphenylphosphine, of 88.7 and 90.9% for bis(o-tolyl)phenylphosphine, of 92.5 and 91.0% for bis(2,5-dimethylphenyl)phenylphosphine and 92.3 for bis(2,4-dimethylphenyl)phenylphosphine are reported. Tris(o-tolyl)phosphine was reported to give a 91.3% iso distribution product, but to be unstable, resulting in less than one percent propylene conversion. "No significant reaction" was reported for tris(o-anisyl)phosphine[tri-o-methoxyphenylphosphine]. See U.S. Pat. No. 4,292,437, Col. 5-7.
Thus, while some success has recently been achieved in obtaining high branched product yields, the art has yet to fully understand which catalyst and reaction characteristics lead to such yields. As a result, many suitable catalysts for obtaining high branched products yields have been overlooked and/or thought to be unsuitable to achieve such yields.